In some fields, particularly in space technology, it is essential to make equipment in such a manner that inevitable breakdowns of components or elements do not give rise to significant degradation of equipment operation. To achieve that object, the general practice is to operate each component or element at its optimum power and to provide redundancy for said components or elements.
Thus, in telecommunications satellites, it is sometimes the practice to use a set of single-beam radiating elements (for transmission or reception) each of which is powered by a signal of well-determined amplitude and phase. Each radiating element is associated with one (or more) power amplifiers. Since the amplitudes of the signals supplied to the radiating elements can vary, it is not always possible to make each associated amplifier operate at its optimum power. To ensure that each amplifier is used under the best conditions, use is made of a "multiport amplifier" configuration.
One such configuration (FIG. 1) comprises an input Butler matrix 10 having a number of input ports 12.sub.1, . . . , 12.sub.n equal to the number of radiating elements (not shown). The sum of the signal power applied to the inputs 12.sub.1, . . . , 12.sub.4 is, in general, constant. The Butler matrix is such that it delivers signals of equal power on its outputs 14.sub.1 to 14.sub.4 (the number of outputs being equal to the number of inputs).
Each output 14.sub.1 of the matrix 10 is associated with a power amplifier 16.sub.i (or a set of such amplifiers) connected to an input 18.sub.i of an output Butler matrix 20. The output matrix has outputs 22.sub.i each of which is connected to a radiating element. The output matrix 20 performs the inverse function to the input matrix 10; thus, on each output 22.sub.i, there is to be found a signal that is the same as the signal applied to the corresponding input 12.sub.i in phase and in amplitude (ignoring an amplification factor).
The amplifiers 16.sub.i all operate at the same power. Naturally, this power corresponds to the optimum operating point. Usually they are identical to one another. To deal with breakdowns, the known configuration as shown in FIG. 1 includes extra amplifiers. Thus, in this example, the configuration has six amplifiers whereas the necessary number is four. The extra amplifiers are initially unused. In the event of breakdown, they are brought into the circuit, by means of switches 24.sub.1, 24.sub.2, . . . , 26.sub.1, 26.sub.2, . . . . For example, amplifier 16.sub.2 ' initially connects output 14.sub.2 of matrix 10 to input 18.sub.2 of matrix 20; after a breakdown is detected in that amplifier, the switches 24.sub.2 and 26.sub.2 are operated to take the amplifier 16.sub.2 ' out of circuit and to bring into circuit the amplifier 16.sub.2 which was previously spare.
The spare amplifiers and the switches, which switches are usually electromechanical, constitute a troublesome increase of mass. In addition, replacing one amplifier by another gives rise to a change of phase due to the change in the path followed by the signals. This alters the signals at the outputs 22.sub.i giving rise to a radiation pattern that is degraded in direction and in amplitude.
The state of the art is also shown by U.S. Pat. No. 5,610,556, in which the configuration includes in each channel between an output of the input matrix and the corresponding input of the output matrix, an amplifier cell comprising two identical amplifiers connected to two input ports of a coupler having a single output port which is connected to the input of the output matrix.
Unfortunately, that device does not make it possible to optimize the power of the cell in the event of one of the amplifiers failing.